A new gibberellin detection system in living cells based on antibody VH/VL interaction

As a new detection method of bioactive gibberellin A4 (GA4) in living cells, a combined system of GA4-dependent interaction of VH and VL composed of a variable region fragment (Fv) of anti-GA4 antibodies and protein-fragment complementation assay (PCA) was developed. First, when VH and VL were displayed in proximity on a phage, they could constitute a functional Fv. Thereafter, VH and VL were shown to interact with each other in a GA4-dependent manner. We then applied this interaction to PCA using GFP as a reporter. VH fused to the C-terminal half of GFP and VL fused to the N-terminal half of GFP were simultaneously expressed in Escherichia coli. The E. coli in which these fusion proteins were inductively produced in the presence of GA4 showed clear GFP fluorescence, while those in the absence of GA4 showed only scarce GFP fluorescence, demonstrating the feasibility of this system to detect GA4 in living organisms.